Clenbuterol and Muscle Growth
Clenbuterol is a β2-adrenergic agonist that is used in horses as a short-term bronchodilator for the management of airway obstruction and for chronic breathing ailments in horses such as Chronic Obstructive Pulmonary Disease (COPD, also known as "heaves"). Clenbuterol’s action as a bronchodilator means that it relaxes the smooth muscle tissue that makes up the airways, allowing for freer breathing.
The United States Food and Drug Administration (FDA) has approved clenbuterol only for use by veterinarians, who may prescribe it to treat horses with the maladies described above. It is also occasionally used as a uterine relaxant for dystocia.1 “The "human equivalent" of clenbuterol is albuterol, which is a prescription-only medication used to treat or prevent bronchospasm caused asthma, bronchitis, emphysema, and other lung diseases, and also to prevent wheezing caused by exercise.”2
There are a variety of proprietary (brand) names for clenbuterol, which is typically offered as an orally-administered syrup. Originally, clenbuterol was given to livestock to increase lean muscle mass and livestock production, but was banned for this purpose due to toxicity issues rising in humans who consumed meat products that were tainted with residual amounts of the drug.
Utility and Popularity
Clenbuterol’s muscle-building properties are tied to its ability to increase the development of skeletal muscle by enhancing muscle protein synthesis.3 Aging decreases skeletal muscle mass and strength, which may be exacerbated by age-related diseases. Clenbuterol dramatically increases skeletal muscle mass in young animals and humans, and partially prevents or restores muscle loss in experimental models of muscle wasting.4 Clenbuterol isn’t a steroid, but it has some properties similar to those of anabolic steroids, such as promoting an increase in muscle mass.
In addition to its ability to increase muscle mass and reduce body fat, clenbuterol remains in the body with an active effect for up to about six days after consumption, while detectable traces can remain longer.5 Because of these properties, clenbuterol has become popular as a weight loss supplement and to enhance athletic performance in humans. Individuals taking clenbuterol for weight loss or performance enhancement often use anabolic steroids or growth hormones as well.
Studies on the efficacy of clenbuterol as a weight loss or performance enhancer in humans are quite limited, although many studies have been performed in animals and livestock:
- Researchers have observed that clenbuterol stimulates muscle growth and repair while preventing atrophy in mice and rats.
- Studies in livestock have indicated that the increase in muscle growth occurs at the expense of fat tissue. This is part of a process referred to as repartitioning.
- A study in horses found that long-term administration of high doses of clenbuterol increased the expression of genes related to various muscle components and fat metabolism.
Despite the fact that there is minimal evidence for clenbuterol as a performance-enhancing drug, it’s listed on the World Anti-Doping Agency’s (WADA) Prohibited List.5
Athletes who use clenbuterol do it to burn fat, build muscle, and improve sports performance, despite the dangers to their health and the possibility that they might be disqualified from sporting events or even banned from their sport for testing positive for performance-enhancing drugs. In fact, athletes who test positive for clenbuterol often claim they must have eaten contaminated meat.5
Proper Application
Clenbuterol can have negative side effects when overused in horses or misused by humans. These can include increased heart rate, rapid breathing, heart palpitations, chest pain, tremors, anxiety and electrolyte imbalance. In horses, side effects are unlikely with clenbuterol, but may include increased heart rate, trembling, excitement, and sweating. It should not be used in horses with heart problems because of the possibility of increased heart rate.
For bronchospasm in equines, the recommended dosage via oral route is typically 0.0008 mg/kg at a concentration of 0.0725 mg/ml, 2 times a day for 3 days. The dosage is increased by ~8mg/kg every 3 days until the horse shows improvement, with a maximum of 30 total days of treatment.
Clenbuterol is FDA-approved for use in horses only and is a prescription-only drug. U.S. federal law restricts this drug to use by or on the written or oral order of a licensed veterinarian. Clenbuterol is prohibited or regulated in most sanctioned equine competitions.
1Plumb’s Veterinary Drugs.
2Drake SD, Hansen LE, Harris C, et al. Effects of clenbuterol on horses. Comp Exerc Physiol. 2013;9(3-4):181-187. doi:10.3920/CEP13022
3Jessen S, Solheim SA, Jacobson GA, et al. Beta -adrenergic agonist clenbuterol increases energy expenditure and fat oxidation, and induces mTOR phosphorylation in skeletal muscle of young healthy men. Drug Test Anal. 2019. doi:10.1002/dta.2755
4W J Carter, W.J., Dang, A.Q., Faas, F.H., Lynch, M.E. Effects of clenbuterol on skeletal muscle mass, body composition, and recovery from surgical stress in senescent rats. Metabolism, 1991 Aug; 40(8):855-60.
About NexGen Pharmaceuticals
NexGen Pharmaceuticals is an industry-leading veterinary compounding pharmacy, offering sterile and non-sterile compounding services nationwide. Unlike other veterinary compounding pharmacies, NexGen focuses on drugs that are difficult to find or are no longer available due to manufacturer discontinuance or have yet to be offered commercially for veterinary applications, but which still serve a critical need for our customers. We also specialize in wildlife pharmaceuticals, including sedatives and their antagonists, offering many unique options to serve a wide array of zoo animal and wildlife immobilization and anesthesia requirements.
Our pharmacists are also encouraged to develop strong working relationships with our veterinarians in order to better care for veterinary patients. Such relationships foster an ever-increasing knowledge base upon which pharmacists and veterinarians can draw, making both significantly more effective in their professional roles.
Disclaimer
The information contained in this blog post is general in nature and is intended for use as an informational aid. It does not cover all possible uses, actions, precautions, side effects, or interactions of the medications shown, nor is the information intended as medical advice or diagnosis for individual health problems or for making an evaluation as to the risks and benefits of using a particular medication. You should consult your veterinarian about diagnosis and treatment of any health problems. Information and statements have not been evaluated by the Food and Drug Administration ("FDA"), nor has the FDA approved the medications to diagnose, cure or prevent disease. Medications compounded by NexGen Pharmaceuticals are prepared at the direction of a veterinarian. NexGen Pharmaceuticals compounded veterinary preparations are not intended for use in food and food-producing animals.
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